Drawing device, especially for plotting instruments for aerial photographs



Sept. 24, K WOLF DRAWING DEVICE, ESPECIALLY FOR PLOTTING INSTRUMENTS FOR AERIAL PHOTOGRAPHS Filed Nov. 24, 1954 United StatesPatent DRAWING DEVICE, ESPECIALLY FOR PLOTTIN G INSTRUMENTS FOR AERIAL PHOTOGRAPHS Kurt Wolf, Oberkochen, Wurttemberg, Germany, assignor to Carl Zeiss, Heidenheim (Brenz), Wurttemberg, Germany The invention concerns a drawing device, especially for plotting instruments for aerial photographs, to be able to establish for example contour lines or also individual points on a drawing sheet. For this purpose the drawing device is guided by the plotting instrument. Especially in the familiar instruments of this kind at beginning of the drawing procedure, the drawing pencil is allowed to fall or is pulled in vertical direction upon the drawing sheet through a mechanism, for example an electromagnet. Thereby the disadvantage arises, that in almost all cases the drawing pencil makes contact too vigorously, so that the graphite tip breaks off. To meet this it has already been attempted to arrange dampers in the drawing device. These, however, effected a too slow or a too soft contact of the drawing pencil, so that the tracing of individual points with the hard graphites required for the rest of the mapping no longer reliably resulted. For eliminating this fault a guide cam also was already provided in familiar drawing devices on which a pin or the like glided with axial movement of the drawing pencil, so that the drawing pencil received a supplementary rotatory movement. Also this construction could not satisfy because the cam rapidly wore out through the contact making of the drawing pencil, so that it happened that the pencil did not reach the drawing sheet, because it had clamped itself on the cam.

All these disadvantages are in accordance with the invention eliminated through the combination of the elements, that the drawing pencil is mounted on a rotatable and axially displaceable carrier, liftable from the same, and that the carrier is guided in ball bearings arranged oblique to its axis. Thereby is achieved, that the drawing pencil already at the slightest contact with the drawing surface can lift itself off from the carrier and is not still further pressed upon the paper by the carrier engaged in downwards movement, and the ball bearings arranged oblique to the axis of the carrier effect that the carrier and therewith also the drawing pencil rotates in the downward movement. After lifting off of the drawing pencil from the carrier the drawing pencil then still carries out several further revolutions, so that also in mapping dots, in spite of the gentle contact of the drawing pencil with the drawing surface a distinct point is drawn.

Advantageously three ball bearings are provided oblique to the axis of the carrier acting on its circumference, of which two are mounted fixed and one displaceable through the force of a spring in direction to the carrier axis. Thereby the advantage is attained, that also after very long use of the drawing device a rotating downwards movement of the carrier and of the drawing pencil is always assured, because every wearing of the obliquely mounted ball bearings is automatically compensated by the moving up of the springily mounted ball bearing. This is then specially appropriate, when an electromagnet is used as means for release of the downwards movement of the drawing pencil, because with such a magnet a lateral starting torque always occurs whereby a one-sided wear of the guide of the carrier for the drawing pencil is occasioned, which made itself unpleasantly noticeable especially in the familiar instruments which provided a gliding guide for the, carrier in that frequently bindings occurred and the drawing pencil did not reach its drawing position. Appropriately the ball bearings each consist of a ring being in friction with the surface of the carrier, the ring for its part running on balls.

The drawing pencil advantageously lies in an axial boring of the carrier, and at least one ring-shaped ball bearing is provided for its guidance. Thereby is assured that the drawing pencil, in spite-of the familiar soiling of its guide by graphite dust, always easily lifts itself from the carrier and further rotates. In further development of the invention the drawing pencil appropriately lies with a disk on the carrier, in order that it with rotation of the carrier through the arising friction acquires a sufiicient momentum for continuing to rotate after lifting off from the carrier.

An example of the object in accordance with the invention is represented in the drawing, namely there is shown in Fig. 1 a section through the drawing device,

Fig. 2 a section along the line II II of Fig. 1,

Fig. 3 a section along the line III-III of Fig. 1, and

Fig. 4 a section along the line IV-IV of Fig. 3.

In Fig. 1 in a housing 1 is mounted an electromagnet 2, which is connected with a not shown current source by a line 3 and upon switching on the current pulls a carrier 4 downwards. After cutting off the current, the carrier 4 is pressed into the position depicted in Fig. l, by a spring 5 whcih lies between the housing 1 and a screw part 6 of carrier 4 closing the upper end of the carrier 4. The carrier 4 shows a boring 7 in which a graphite holder 8 is mounted. The graphite holder 8, with a disk 9 fastened to it, rests on the carrier 4 so that it can be lifted off. The carrier 4 and housing 1 further show two ball bearings 10 and 11 arranged ring-shaped for guiding the graphite holder 8. In the graphite holder 8 is inserted a pencil lead 12 which with lowering of the graphite holder 8 seats itself on a drawing sheet 13. In the housing 1 are mounted three ball bearings 14, 15, 16 (Fig. 2) which serve for guiding the carrier 4. As represented in Fig. 4, the ball bearings consist of a ring 17 which runs on balls 18, and they are fastened to oblique bodies 20, 21, and 22 by means of screws 19 as represented in Fig. 3 for the ball bearing 14. The body 22 is connected with the housing 1 by a screw 23 and is rotatable about the axis of the screw 23. A spring 24 continually pushes against a pin 25 of the body 22 and presses this and therewith the ball bearing 16 continually against the carrier 4.

The mode of action of the device is as follows:

With switching on a current the electromagnet 2 pulls the carrier 4 downwards. Thereby this executes a rotatory movement, which is transmitted to it by the ball bearings 14, 15, and 16 arranged oblique to its axis. The springily constructed ball bearing 16 thereby takes care that all three ball bearings 14, 15, and 16 always lie against the carrier 4. The graphite holder 8 by reason of the force of gravity acting on it and the thereby effected friction contact between the disk 9 and the screw part 6 executes the same movement until the graphite point 12 is seated on the drawing sheet 13. With further downward movement of the carrier 4 the graphite holder 8 stops, the disk 9 separates itself from the screw part 6 and the graphite holder independently of the further movement of the carrier 4 can execute continued revolutions so that a sharp point is depicted on the drawing sheet 13. This continued rotatory movement is aided by the ball bearings 10 and 11. If the circuit is broken, then the spring 5 pushes the carrier 4 back into the position depicted in Fig. 1, whereby the carrier 4 lifts the graphite holder 8 off from the drawing sheet.

l l i 1, .1 I

l 1. In a drawing device, especially for plotting instruments for aerial photographs, a carrier arranged rotatable and axially displaceable, a drawing pencil lying liftable on 'saidearrien'bali bearings for guidingsaid 'car rierin movin'g, said ball 'bearin'gsbeing arranged with their axes oblique to the 'axisof saidcarrier to efie'ct a screw motion of the carrier in displacing axially, means to effect the axially displace'rnntiof said carrier,

2. Drawing deviceaccording'to-claim 1, characterized in that three ballbear'ings are provided, acting 'on the circumference of saidlearrier oblique to the axis of said carrier, of which two are 'mounted;-fiXedly and one is displaceable, and that a spring is provided acting upon saiddisplacable'hall bearing in directionto the carrier axis. 7 V 3.-'Drawing device acc ording' to claim 1, characterized in that the said ball bearings each consist of a ring being in friction with the'surface of said carrier, and balls upon which said'ring forits 'part is running.

4. Drawing device according to claim 1, characterized in that said carrier has an axial boring, said drawing pencil lying in that boring and that at least one ring-shaped further ball bearing is provided for the guidance of the said drawing pencil in the carrier.

5. Drawing device according to claim 1, characterized in, that said drawing pencil has a disk, said disk lying on a part of said carrier.

References Cited in the file of this patent UNITED STATES PATENTS 2,043,596 Rovick June 9, 1936 2,166,608 Postlewaite July 18, 1939 2,187,929 Blane Jan. 23, 1940 2,522,756 Hall Sept. 19, 1950 2,541,435 NOCk Feb. 13, 1951 V v FOREIGN PATENTS 875,060 France June 1, 1942 

